Dehydroepiandrosterone (DHEA) metabolism in Saccharomyces cerevisiae expressing mammalian steroid hydroxylase CYP7B: Ayr1p and Fox2p display 17β-hydroxysteroid dehydrogenase activity

Abstract

We have engineered recombinant yeast to perform stereospecific hydroxylation of dehydroepiandrosterone (DHEA). This mammalian pro-hormone promotes brain and immune function; hydroxylation at the 7α position by P450 CYP7B is the major pathway of metabolic activation. We have sought to activate DHEA via yeast expression of rat CYP7B enzyme. Saccharomyces cerevisiae was found to metabolize DHEA by 3β-acetylation; this was abolished by mutation at atf2. DHEA was also toxic, blocking tryptophan (trp) uptake: prototrophic strains were DHEA-resistant. In TRP+ atf2 strains DHEA was then converted to androstene-3β,17β-diol (A/enediol) by an endogenous 17β-hydroxysteroid dehydrogenase (17βHSD). Seven yeast polypeptides similar to human 17βHSDs were identified: when expressed in yeast, only AYR1 (1-acyl dihydroxyacetone phosphate reductase) increased A/enediol accumulation, while the hydroxyacyl-CoA dehydrogenase Fox2p, highly homologous to human 17βHSD4, oxidized A/enediol to DHEA. The presence of endogenous yeast enzymes metabolizing steroids may relate to fungal pathogenesis. Disruption of AYR1 eliminated reductive 17βHSD activity, and expression of CYP7B on the combination background (atf2, ayr1, TRP+) permitted efficient (>98%) bioconversion of DHEA to 7α-hydroxyDHEA, a product of potential medical-utility. Copyright © 2002 John Wiley & Sons, Ltd.